1. Field of the Invention
The present invention relates to a welding tool for a friction-stir welding apparatus for friction-stir welding a plurality of members to be welded, and particularly to a welding tool for spot friction-stir welding hard members to be welded such as steel members.
2. Description of the Related Art
As an apparatus for welding a plurality of members to be welded, there is a friction-stir welding apparatus available. The apparatus arranges a welding tool at a part to be welded of an article composed of stacked members. Next, the apparatus presses the welding tool against the part to be welded while rotating the welding tool and immerses the front end of the welding tool into the part to be welded. The welding tool rotates while the front end thereof is pressed against the part to be welded. By doing this, frictional heat is produced, thereby the part to be welded is softened, and the boundary part of each member to be welded is stirred. Hereafter, each stirred boundary part is solidified and each member is welded.
When each member to be welded is made of an aluminum alloy, the front end of the welding tool is little worn away. Therefore, one welding tool can weld a plurality of parts to be welded in different locations. However, when a member to be welded is a hard member such as a steel member, the front end of the welding tool is worn away remarkably. Therefore, parts which can be welded by one welding tool decreases and the exchange frequency of the welding tool increases. As a conventional art for solving this problem, a welding tool having a front end made of a highly wear resistant material is disclosed, for example, in Japanese Patent Laid-Open Publication No. 2003-532542.
In the welding tool of the related art disclosed in the patent publication aforementioned, a shank which is a base end is formed separately from a pin section which is a front end and a shoulder section. Further, a ring collar member clamps both the outer peripheral surface of the shank and the outer peripheral surface of the shoulder section, so that the shank, the pin section, and the shoulder section are fixed mechanically. For example, the collar member clamps the shank and the shoulder section by a fixing method such as shrinkage fit or press fit.
In the related art, when the pin section or the shoulder section is worn away, it is difficult to exchange only the pin section and the shoulder section independently from the shank, and it is necessary to exchange the whole welding tool. Therefore, the expense caused by the exchange of the welding tool increases, thereby the welding cost inevitably increases.